NSF/EAR-BSF: Resolving slow slip transients before and after the 2011 Tohoku-oki earthquake with geodesy and seismicity

构造板块运动在会聚板块边界产生应力积累，并通过断层滑动释放。有些断层在地震时快速滑动，产生地震波，这是地震学家传统上分析的。其他断层的滑动速度要慢得多，而且不产生地震波。断层以约100倍于长期构造加载速率的速率滑动长达数周的事件通常被称为慢滑动事件（SSE）。SSE通常伴随着弱地震活动，分析它们需要来自敏感的大地测量和地震网络的数据。SSE被认为在破坏性地震的引发中发挥着重要作用，因此阐明控制其行为的物理学非常重要。大地测量仪器的进步已经能够检测到几次大地震前发生的SSE，其中2011年3月11日东北冲9.0级地震是历史上记录最好的事件。日本东北部的时空地震大地测量网络覆盖范围提供了一个独特的机会，研究导致这一大推力地震及其后果的复杂活动。到目前为止，所报告的前兆观测结果多种多样，从GPS观测到的十年滑动加速到主震前两天的最终前震序列。本项目将对东北冲地震前几十年的地震和地震滑动相互作用进行更精确的描述。该项目的研究人员开发了一种创新方法，可以使用大地测量和地震活动数据检测低振幅SSE。这项研究的结果将为改善所有会聚板块边界的短期地震危险评估提供信息。该项目是与日本研究人员和以色列特拉维夫大学一名新教员通过两国NSF-BSF计划进行的国际合作。本项目旨在分析2011年3月11日东北冲置9.0级大地震前后几十年来的地震瞬时滑动细节。通过使用大地匹配滤波器技术，我们试图检测低振幅的瞬变事件在大地时间序列比以前开发的技术所观察到的。研究人员将使用现有的和新的方法来同时分析大地测量和地震观测，因为它们可能提供有关共同物理现象的补充信息。该方法将首先应用于南海海槽，在那里已经描述了许多慢滑事件，作为一种校准和实验，在一种新的检测技术相结合的GPS和倾斜仪数据。其次，他们将在东北地区寻找短暂的活动，重点是两个地区，即三陆近海和房总半岛下方。在三陆近海，重复发生的地震显示出滑动率的振荡，这仍然需要通过大地测量观测来捕捉，以确定其空间和时间范围。在房总半岛下面，一系列缓慢滑动事件正在发生，其复发间隔受到东北冲地震的干扰，地震活动和大地测量记录将被整合，以检测低振幅瞬态信号，并提高现有滑动模型的分辨率。一个主要目标将是解决东北地震应力扰动的周期和动力学的慢滑事件的影响。最后，研究人员将开发一个日本东北部规模的地震和抗震级联事件导致M9.0东北冲地震的综合模型。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Tectonic plate motions produce stress accumulation at convergent plate boundaries, which is released by slip on faults. Some faults slip rapidly during earthquakes, generating waves, traditionally analyzed by seismologists. Other faults slip at much slower rates and aseismically, without generating waves. An episode during which the fault slips at rates that are about 100 times the long-term tectonic loading rate for periods of up to several weeks is commonly referred to as a slow slip event (SSE). SSEs are often accompanied by weak seismic activity and analyzing them requires data from sensitive geodetic and seismic networks. SSEs are thought to play an important role in the initiation of damaging earthquakes, and it is therefore important to elucidate the physics that controls their behavior. Advances in geodetic instrumentation have enabled the detection of SSEs occurring before several large earthquakes, among which the March 11, 2011 M9.0 Tohoku-oki earthquake is the best-recorded event in history. The spatiotemporal seismo-geodetic network coverage of northeast Japan provides a unique opportunity to study the complex activity leading up to this megathrust earthquake and in its aftermath. Precursory observations reported thus far are very diverse, ranging from a decadal slip acceleration observed by GPS to a final foreshock sequence two days before the main shock. This project will develop a more precise picture of seismic and aseismic slip interactions in the decades before the Tohoku-oki earthquake. The researchers on this project have developed an innovative method which enables the detection of low-amplitude SSEs using geodetic and seismicity data. The results from this research will inform efforts to improve short-term earthquake hazard assessments in all convergent plate boundaries. This project is an international collaboration with researchers in Japan and with a new faculty member at the Tel Aviv University in Israel, through the binational NSF-BSF program. This project aims to analyze the details of aseismic transient slip in the decades leading up to, as well as following the great March 11, 2011 M9.0 Tohoku-oki megathrust earthquake. By using a geodetic matched filter technique, we seek to detect lower-amplitude transient events in geodetic time series than the ones observed with previously developed techniques. The researchers will use existing and new methods to simultaneously analyze geodetic and seismological observations, as they are likely to provide complementary information about a common physical phenomenon. The methodology will be applied first to the Nankai trough, where many slow slip events have already been described, as a calibration and as an experimentation in combining GPS and tilt-meter data in a novel detection technique. Secondly, they will search for transient activities in the Tohoku area, with a focus on two areas, offshore Sanriku and beneath the Boso Peninsula. Offshore Sanriku, repeating earthquakes have shown oscillations in slip rates that still have to be captured by geodetic observation to determine their spatial and temporal extent. Beneath the Boso Peninsula, where a sequence of slow slip events with recurrence intervals disturbed by the Tohoku-oki earthquake is going on, seismicity and geodetic recordings will be integrated to detect lower-amplitude transient signals and to improve the resolution of existing slip models. A primary goal will be to resolve the impact of the Tohoku earthquake stress perturbation on the cycle and dynamics of the slow slip events. Finally, the researchers will develop a comprehensive model at the scale of northeast Japan of the seismic and aseismic cascade of events leading up to the M9.0 Tohoku-oki earthquake.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.